A hybrid vehicle may provide regenerative driveline braking to slow a vehicle. During regenerative braking, a vehicle's kinetic energy may be converted to electrical energy. The electrical energy is stored in an energy storage device where it may be held until it is needed to supply power to the vehicle or perform some other function. The energy storage device may have capacity constraints so that it may store a limited amount of electrical energy. Consequently, it may not be desirable to continue to convert the vehicle's kinetic energy into electrical energy even though conditions are favorable to produce electrical energy. The driveline may transition from a regeneration mode to an engine braking mode to maintain driveline braking when it is not desirable to continue regeneration. However, transitioning from regenerative braking to engine braking may produce driveline torque disturbances.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for controlling driveline braking, comprising: providing driveline braking via an electric machine while rotation of an engine is stopped; and adjusting a torque of the electric machine in response to a condition of the engine.
By adjusting torque of an electric machine in response to a condition of an engine, it may be possible to provide an amount of driveline braking via the electric machine that is equivalent to an amount of engine braking that may be provided by the engine. Therefore, if the energy storage device becomes fully charged and the driveline transitions from regenerative braking to engine braking, a constant level of driveline braking may be provided.
The present description may provide several advantages. Specifically, the approach may reduce driveline torque disturbances of a hybrid driveline. Further, the approach may improve vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.